The immune system of humans and other mammals is responsible for providing protection against infection and disease. Such protection is provided both by a humoral immune response and by a cell-mediated immune response. The humoral response results in the production of antibodies and other biomolecules that are capable of recognizing and neutralizing foreign targets (antigens). In contrast, the cell-mediated immune response involves the activation of macrophages, neutrophil, natural killer cells (NK), and antigen-specific cytotoxic T-lymphocytes by T cells, and the release of various cytokines in response to the recognition of an antigen.
The ability of T cells to optimally mediate an immune response against an antigen requires two distinct signaling interactions. First, antigen that has been arrayed on the surface of antigen-presenting cells (APC) must be presented to an antigen-specific naive T cells in the form of MHC: peptide complex (1, 2). Such presentation delivers a signal via the T cell receptor (TCR) that directs the T cell to initiate an immune response that will be specific to the presented antigen. Second, a series of co-stimulatory signals, mediated through interactions between the APC and distinct T cell surface molecules, triggers first the activation and proliferation of the T cells and ultimately their inhibition (3-5). Thus, the first signal confers specificity to the immune response whereas the second signal serves to determine the nature, magnitude and duration of the response while limiting immunity to self. Of particular importance among these second signal molecules is binding between the B7.1 (CD80) (6) and B7.2 (CD86) (7-9) ligands of the Antigen Presenting Cell and the CD28 and CTLA4 receptors (10-12) of the T-lymphocyte.
Cytotoxic T lymphocyte antigen-4 (CTLA4) is recognized as a key regulators of adaptive immune responses, having a central role in the maintenance of peripheral tolerance and in shaping the repertoire of emergent T cell responses and, therefore, a therapeutic target for the treatment of cancer and inflammation. Treatment with anti-CTLA4 antibodies has been shown to be a powerful tool for enhancing anti-tumor immunity in preclinical models (10). Monotherapy with an antibody against CTLA4 promoted rejection of transplantable tumors of various origins.
Based on promising preclinical tumor model studies, the clinical potential of antibodies against CTLA4 has been explored in different human malignancies. Although anti-CTLA4 (Ipilimumab, marketed as Yervoy) has demonstrated efficacy in treating melanoma, treatment and targeting of CTLA4 is associated with autoimmune like toxicities. Characteristic side effects from inhibition of CTLA4 are generally called immune-related adverse events (irAEs) and the most common irAEs are skin rash, hepatitis, colitis and endocrinopathies, particularly hypopituitarism. Therefore, there is a desire to improve the therapeutic potential of anti-CTLA4 antibodies by increasing efficacy while reducing the associated irAEs.
Another focus for the field of immunotherapy and the treatment of tumors, is the combination of different immune check inhibitors in order to enhance anti-tumor activity, particularly against poorly immunogenic tumors. However, this approach is associated with the risk of further increasing the autoimmune side effects further highlighting the need to selectively modulate cancer immunity without enhancing autoimmunity.
Further investigations into the ligands of the CD28 receptor have led to the identification and characterization of a set of related B7 molecules (the “B7 Superfamily”) (32-33). There are currently several known members of the family: B7.1 (CD80), B7.2 (CD86), the inducible co-stimulator ligand (ICOS-L), the programmed death-1 ligand (PD-L1; B7-H1), the programmed death-2 ligand (PD-L2; B7-DC), B7-H3, B7-H4 and B7-H6 (35-36). B7-H1 is broadly expressed in different human and mouse tissues, such as heart, placenta, muscle, fetal liver, spleen, lymph nodes, and thymus for both species as well as liver, lung, and kidney in mouse only (37). B7-H1 (PD-L1, CD274) is a particularly significant member of the B7 Superfamily as it is pivotally involved in shaping the immune response to tumors (38; U.S. Pat. Nos. 6,803,192; 7,794,710; United States Patent Application Publication Nos. 2005/0059051; 2009/0055944; 2009/0274666; 2009/0313687; PCT Publication No. WO 01/39722; WO 02/086083).
Programmed Death-1 (“PD-1”) is a receptor of B7-H1 as well as B7-DC. PD-1 is a type I membrane protein member of the extended CD28/CTLA4 family of T cell regulators (39; United States Patent Application Publication No. 2007/0202100; 2008/0311117; 2009/00110667; U.S. Pat. Nos. 6,808,710; 7,101,550; 7,488,802; 7,635,757; 7,722,868; PCT Publication No. WO 01/14557). Compared to CTLA4, PD-1 more broadly negatively regulates immune responses. PD-1 is expressed on activated T cells, B cells, and monocytes (40-41) and at low levels in natural killer (NK) T cells (42-43).
Interaction of B7-H1 and PD-1 has been found to provide a crucial negative co-stimulatory signal to T and B cells (43) and functions as a cell death inducer (39). The role of B7-H1 and PD-1 in inhibiting T cell activation and proliferation has suggested that these biomolecules might serve as therapeutic targets for treatments of inflammation and cancer. Consequently, the use of anti-PD1 and anti-B7-H1 antibodies to treat infections and tumors and up-modulate an adaptive immune response has been proposed and demonstrated to be effective for the treatment of a number of human tumors. However, not all subjects respond or have complete responses to anti-PD-1 or anti-B7-H1 treatment and so there is a strong interest in combining anti-PD-1 or anti-B7-H1 antibodies with other immune check inhibitors in order to enhance anti-tumor activity.
4-1BB (also known as CD137 and TNFRSF9) is another immune checkpoint molecule. The best characterized activity of CD137 is its costimulatory activity for activated T cells. Crosslinking of CD137 enhances T cell proliferation, IL-2 secretion, survival and cytolytic activity. Further, like anti-CTLA4, anti-4-1 BB antibodies can enhance immune activity to eliminate tumors in mice (27-29). However, unlike the tendency of anti-CTLA4 antibodies to exacerbate autoimmune diseases, cancer therapeutic anti-4-1 BB mAbs have been shown to abrogate the development of autoimmune diseases in lupus prone mice, in which they inhibited anti-dsDNA antibody production and reduced the renal pathology (25, 26). Previously data have demonstrated that it is possible to reduce the autoimmune side effects of anti-CTLA4 treatment in a mouse colon cancer tumor model by combining treatment of anti-CTLA4 with anti-4-1 BB antibody, while enhancing the anti-tumor activity (19). This demonstrates that it is possible to offset the autoimmune side effects of anti-CTLA4 tumor therapy.
Preclinical screening of anti-human CTLA4 antibodies is fraught with difficulty because in vitro immunological correlates are sometimes of little value, as demonstrated by experience with anti-mouse CTLA4 antibodies. The same anti-mouse CTLA4 antibodies that induce potent anti-tumor immunity in vivo can have variable effects on T cells in vitro. Anti-CTLA4 antibodies enhanced T cell proliferation in response to alloantigen, but suppressed T cell proliferation in response to costimulation by anti-CD 28 (30, 31). Also, CTLA4 engagement with antibody could either promote or inhibit proliferation of different subsets of T cells in the same culture (32). This complication can be overcome if one can study human T cell responses in a rodent model.
Described herein are anti-CTLA4 antibodies with reduced autoimmune side effects when used to enhance immune responses and for use in anti-tumor therapy. Furthermore, these antibodies can be used in combination with other checkpoint inhibitors, such as anti-PD-1 and anti-4-1 BB, to enhance anti-tumor while abrogating autoimmune side effects.